Resin materials for electronic components used for a semiconductor encapsulating material, an insulating layer for multilayer printed boards, and the like include various resins such as an epoxy resin, a cyanate ester resin, a bismaleimide-triazine resin, a benzoxazine resin, and the like. These resin materials are required to have various performances such as heat resistance, thermal decomposition resistance, flame retardance, moisture resistance/solder resistance, dielectric characteristics, etc.
Among the various resin materials, the benzoxazine resin is excellent in characteristics such as heat resistance and dielectric characteristic of a cured product. Specifically, there are known a benzoxazine resin produced by reacting bisphenol with formalin and aniline (refer to Patent Literature 1), a polymer compound having a benzoxazine ring in a main chain (refer to Patent Literature 2 and Patent Literature 3), and the like. However, the benzoxazine resin described in Patent Literature 1 is insufficient in heat resistance, flame retardance, moisture resistance/solder resistance, and dielectric characteristics, and a benzoxazine resin containing, as a base, the polymer compound described in Patent Literatures 2 and 3 has poor fluidity, poor moldability as a semiconductor encapsulating material, and poor impregnation in a glass cloth for producing a prepreg, and a curable composition of the resin has the problem of poor handling property and insufficient heat resistance in application to the electronic materials described above. Therefore, there has been demand for development of a resin composition being excellent in any one of heat resistance, fluidity, moisture resistance/solder resistance, flame retardance, and dielectric characteristics and having good performance balance.